The present invention relates to enamels for coating steel articles with a view to afford protection to same from the effect of aggressive media such as acids and alkalis. The aforesaid steel articles can be pipes, reactors, heat exchangers and other vessels.
The prior art teaches an enamel for coating steel articles comprising SiO.sub.2, Al.sub.2 O.sub.3, CaO, Na.sub.2 O, K.sub.2 O, B.sub.2 O.sub.3, TiO.sub.2, Li.sub.2 O, ZrO.sub.2, CaF.sub.2, CuO and SrO with the following ratio of said components, in percent by weight:
______________________________________ SiO.sub.2 50 to 80 Al.sub.2 O.sub.3 0.5 to 6 CaO 0.2 to 5 Na.sub.2 O 7 to 20 K.sub.2 O up to 5 B.sub.2 O.sub.3 0.2 to 6 TiO.sub.2 up to 5 Li.sub.2 O 0.2 to 5 ZrO.sub.2 0.2 to 10 CaF.sub.2 0.2 to 7 CuO 0.5 to 20 SrO 0.2 to 10 ______________________________________
The disadvantages of the enamel known in the art are the use of a large number of components, as well as a large amount of copper oxide which may result in metallization of the coating and deterioration of its protective properties. In addition, copper oxide is toxic.